Folate receptor binding conjugates of antifolates

ABSTRACT

Conjugates of antifolates, releasable linkers, and drugs, and pharmaceutical compositions containing them are described. The conjugates are useful for treating diseases arising from pathogenic cell populations. Methods for treating stroll diseases are also described.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. application Ser. No. 14/919,518, filedOct. 21, 2015, pending, which is a continuation of U.S. application Ser.No. 14/010,122 filed Aug. 26, 2013, now U.S. Pat. No. 9,192,682, whichis a continuation of U.S. application Ser. No. 13/063,889, filed Mar.14, 2011, now U.S. Pat. No. 8,546,425, which is a National Stage Entryunder 35 U.S.C. § 371 of International Application No.PCT/US2009/057363, filed Sep. 17, 2009, which claims the benefit under35 U.S.C. § 119(e) of U.S. Provisional Application Ser. No. 61/097,655,filed Sep. 17, 2008, the entirety of the disclosure of each of which isincorporated herein by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

Folic acid (FA), or vitamin B9, is an essential nutrient required by allliving cells for proper metabolic maintenance of 1-carbon pathways aswell as for nucleotide biosynthesis. This ligand displays extremely highaffinity (KD˜100 pM) for a cell surface-oriented glycoprotein called thefolate receptor (FR), which is a glycosylphosphatidyinositol-linkedprotein that captures its ligands front the extracellular milieu. Thefolate receptor (FR) is a tumor-associated membrane protein that bindsfolic acid (FA) and is capable of transporting molecules bound to folicacid inside cells via an endocytosis mechanism. Immediately afterbinding, the plasma membrane surrounding the FR-ligand complex willinvaginate to form an internal vesicle, called an endosome. The pH ofthe vesicle lumen is somewhat lowered through the action of proton pumpsthat are co-localized in the endosome membrane, and this acidificationpresumably mediates a conformational change in the FR protein to releaseits bound ligand to allow for cytosolic entry. The FR is also arecognized tumor antigen; and because of this, methods to exploit itspresence and function have been explored for possible therapeutic value.

FR-α distribution in normal adult tissue is restricted to the apicalmembrane surface of some polarized epithelial cells, including lung,choroid plexus and some glandular tissue. Expression is also high inplacental trophoblasts and on the luminal surface of proximal tubulekidney epithelial cells, the latter probably being important for there-absorption of folates from the urine. However, Elevated expression ofthe FR-α occurs in several cancer types. Non-mucinous ovarian cancer(the majority of ovarian cancers) was the tumor type first to beassociated with “over-expression”. Several studies confirmed that˜80-90% of these tumors oven-express FR-α. Other gynecological cancers(e.g. ˜50% of serous uterine tumors) also over-express the receptor.Although the endometrioid histologic subtype may express the receptorless frequently, it is by far the most common form of uterine cancer.Therefore, it is believed herein that a considerable number of uterinecancer patients may benefit from some form of FR-targeted therapy. Othertumors reported to over-express FR-α to varying frequencies includepediatric ependymal brain tumors, breast, colon, renal and lung tumors,and mesothelioma.

Although it is generally accepted that FA can be conjugated to virtuallyany molecule to mediate delivery inside FR-positive, cells, not allconjugates can be expected to bind to the FR with the same affinity. Itis believed herein for example that large drugs that are linked in closeproximity to the FA moiety may, perhaps due to steric interactions,alter the ability of FA to enter the binding pocket of the FR. Further,the nature of the drug may also be important, because intramolecularassociation with the FA might yield a poorly-binding conjugate that maynot properly orient itself into the FR. In any case, after FA hasdelivered the molecule to the target site, it is no longer used.Therefore, it was recognized herein that targeting with a differentmolecule that had the potential to have a second function in treating adisease state would be useful.

It has been discovered herein that antifolates are also capable oftargeting FR, and in conjunction with releasable linkers are alsocapable of targeted delivery of molecules to cells that express the FR.However, it has been reported that the relative affinity of suchantifolates is widely varying, as determined at 4° C., which hashindered the use of antifolates as targeting ligands. It has also beenunexpectedly discovered herein that the relative affinity of antifolatesat the folate receptor, as compared to folic acid, is temperaturedependent. Moreover, it has been discovered that the relative affinityof some antifolates increases with increasing temperature, while therelative affinity of other antifolates decreases with increasingtemperature. Further, the relative affinity of still other antifolatesis relatively invariant with increasing temperature.

Described herein are compounds, compositions, and methods that includeconjugates comprising a folate receptor binding antifolate, at least onereleasable linker, and one or more drugs, where the antifolate has ahigh relative affinity for the folate receptor, as compared to folicacid, at temperatures above 4° C., such as at temperatures above 20° C.,at temperatures above 25° C., at temperatures above 30° C., and/or attemperatures that are physiologically relevant, such as physiologicaltemperatures in mammals. Also described herein are compounds,compositions, and methods that include conjugates comprising a folatereceptor binding antifolate, at least one releasable linker, and one ormore drugs, where the conjugate has a high relative affinity for thefolate receptor, as compared to folic acid, at temperatures above 4° C.,such as at temperatures above 20° C., at temperatures above 25° C., attemperatures above 30° C., and/or at temperatures that arephysiologically relevant, such as physiological temperatures in mammals.In general, the conjugates described herein are covalent conjugates;however, it is to be understood that the drugs forming part of theconjugates described herein may include other bond forms, including butnot limited to complexes, such as metal chelates, and the like.

In one embodiment, compounds, compositions, and methods are describedherein that include a conjugate comprising an antifolate having arelative affinity for the folate receptor, as compared to folic acid, ofat least about 0.1, at least about 0.2, at least about 0.25, or at leastabout 0.5, at one or more of the temperatures described herein. Inanother embodiment, compounds, compositions, and methods are describedherein that include a conjugate having a relative affinity for thefolate receptor, as compared to folic acid, of at least about 0.05, atleast about 0.1, at least about 0.2, at least about 0.25, or at leastabout 0.5, at one or more of the temperatures described herein.

In another embodiment, a method for evaluating the folate receptorbinding ligand affinity for the FR is described herein. In one aspect,the binding affinity is relative and is compared with folic acid. It isto be understood that the assays described herein may be used toevaluate the relative selectivity and/or specificity of the binding tothe folate receptor by competing the folate receptor binding ligandand/or conjugate with folic acid. It is appreciated that such relativeaffinities may be used to select molecules capable of binding to the FRand to select conjugates that include FR receptor binding moieties.

In another embodiment, compounds, compositions, and methods aredescribed herein that include a drug delivery conjugate of the formulaAL(D)_(m)are described wherein A is a folate receptor binding antifolate; L is amonovalent or multivalent linker, comprising at least one releasablelinker; each D is a drug; and m is an integer from 1 to about 3. It isto be understood that when m is greater than 1, each drug D isindependently selected in each instance, in other words, D may be thesame drug or be different drugs in each instance.

In another embodiment, the compositions and methods described herein areuseful for treating one or more pathogenic populations of cells in apatient. The compositions include a therapeutically effective amount ofone or more conjugates described herein, optionally in combination withone or more carriers, excipients, and/or diluents, or any combinationsthereof. The methods include the step of administering an effectiveamount of one/or more conjugates described herein and/or one or morecompositions described herein, In another embodiment, the compositionsand methods are useful for treating cancer, and other diseases.

In another embodiment, uses of the compounds and compositions in themanufacture of medicaments are described herein, where the medicamentsinclude a therapeutically effective amount of one or more conjugatesdescribed herein and/or one or more compositions described herein fortreating one or more pathogenic populations of cells in a patient. It isto be understood that the medicaments may be used in any of the methodsdescribed herein for treating one or more pathogenic populations ofcells in a patient.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Panel A, KB cell-based relative affinity assay. Panel B,cell-free relative affinity assay (isolated plate-bound folatereceptor). Both assays were performed in the absence of serum while theplates were sitting on a bed of ice. FA, (●). EC145, (▪).

FIG. 2. Panel A. Pte acid on ice, Panel B, Pte at 37° C. Panel C, LV onice, Panel B, LV at 37° C. Each assay was conducted using adherent KBcells as the FR source without serum in the test medium. FA=Pte-γGlu,(●); LV, (∘); Pte (▪).

FIG. 3. Panel A, EC72 on ice. Panel B, EC72 at 37° C. Panel C, EC17 onice. Panel B. EC17 at 37° C. Each assay was conducted using adherent KBcells as the FR source without serum in the test medium. FA, orPte-γGlu, (●); EC72, (∘); EC17 (▪).

FIG. 4. Panel A, binding of PA to KB cells in the presence of increasingamounts of fetal bovine serum (FBS). Panels B and C, RA of FA and EC145,respectively (percent serum: 0% (●), 10% (▪), 25% (▴), 50% (□), 75% (∇),100% (∘)). Panel B effect of 0% or 10% serum on the RA of EC140.

FIG. 5. Activity of compounds against subcutaneous KB tumors (2 μmol/kgTIW/2weeks; vertical dotted line indicates last day of dosing): (a)Controls; (b) EC0282 (CB3717) 0/5 complete responses; (c) EC145 2/5complete responses; (d) EC0284 5/5 complete responses.

FIG. 6. Percent change in weight of treated animals in each test group.(2 μmol/kg TIW/2 weeks; vertical dotted line indicates last day ofdosing): (a) Controls; (b) EC0282 (CB3717) 0/5 complete responses; (c)EC145 2/5 complete responses; (d) EC0284 5/5 complete responses.

FIG. 7. Relative affinity assay (10% serum/FDRPMI): FA (●) 1.000; EC284(▪) 0.148; EC283 (∘) 0.002.

FIG. 8. Relative affinity assay (10% serum/FDRPMI); (a) FA (●) 1.000;(b) EC282 (●) 0.148

FIG. 9. Activity of EC282 against KB cells (72 h continuous Assay);Panel A. IC₅₀ 5 nM. Panel B. IC₅₀ 19 nM.

FIG. 10. Activity of EC0284 against KB cells (2 h treatment/72 h Assay):(a) EC0284+excess folic acid; (b) EC0284.

DETAILED DESCRIPTION

In one embodiment, drug delivery conjugates of the formulaAL(D)_(m)are described wherein A is a folate receptor binding antifolate; L is amonovalent or multivalent linker, comprising at least one releasablelinker; each D is a drug; and m is an integer from 1 to about 3. It isto be understood that when m is greater than 1, each D may be the samedrug or be a different drug from another in each instance. In anotherembodiment, the monovalent or multivalent linker L includes at least tworeleasable linkers. In one variation of each of the foregoing, themonovalent or multivalent linker includes at least one releasable linkerthat is not a disulfide.

In another embodiment, the conjugates described herein include anantifolate having a relative affinity for the folate receptor, ascompared to folic acid, of at least about 0.1, at least about 0.2, atleast about 0.25, or at least about 0.5, at one or more of thetemperatures described herein. In another embodiment, the conjugatesdescribed herein have a relative affinity for the folate receptor, ascompared to folic acid, of at least about 0.05, at least about 0.1, atleast about 0.2, at least about 0.25, or at least about 0.5, at one ormore of the temperatures described herein. In another embodiment, thecompounds, compositions, and methods that include conjugates comprisinga folate receptor binding antifolate, at least one releasable linker,and one or more drugs, where the antifolate has a high relative affinityfor the folate receptor, as compared to folic acid, at temperaturesabove 4° C., such as at temperatures above 20° C., at temperatures above25° C., at temperatures above 30° C., and/or at temperatures that arephysiologically relevant, such as physiological temperatures in mammals.Also described herein are compounds, compositions, and methods thatinclude conjugates comprising a folate receptor binding antifolate, atleast one releasable linker, and one or more drugs, where the conjugatehas a high relative affinity for the folate receptor, as compared tofolic acid, at temperatures above 4° C., such as at temperatures above20° C., at temperatures above 25° C., at temperatures above 30° C.,and/or at temperatures that are physiologically relevant, such asphysiological temperatures in mammals. In general, the conjugatesdescribed herein are covalent conjugates; however, it is to beunderstood that the drugs forming part of the conjugates describedherein may include other bond forms, including but not limited tocomplexes, such as metal chelates, and the like.

It is to be understood that the determination of the relative affinityof the antifolates and/or conjugates described herein may be performedby any conventional method, or alternatively by the methods describedherein adapted for measuring relative affinity at temperatures above 4°C., such as at temperatures above 20° C., at temperatures above 25° C.,at temperatures above 30° C., and/or at temperatures that arephysiologically relevant, such as physiological temperatures in mammals.

As used herein, the term “antifolate” generally refers to any compoundthat is an inhibitor, antagonist or other modulator of folatemetabolism, such as inhibition and/or antagonism of dihydrofolatereductase (DHFR), glycinamide ribonucleotide transformylase (GARTF),folylpolyglutamate synthetase (FPGS), and thymidylate synthase (TS), ora folate receptor antagonist. It is appreciated that antifolates maybind to the folate binding site in any of the above, or to another sitethat influences binding of folate or another compound to the folatebinding site of any of the above. As used herein, the term “folatereceptor binding” generally refers to compounds that selectively orspecifically bind to the folate receptor.

In another embodiment the folate receptor binding antifolate is selectedfrom LV, L-leucovorin (L-5-formyltetrahydrofolate); 5-CH3-THF,5-methyltetrahydrofolate; FA, folic acid; PteGlu, pteroyl glutamate(FA); MTX, methotrexate; 2-dMTX, 2-desamino-MTX; 2-CH3-MTX,2-desamino-2-methyl-MTX; AMT, aminopterin; 2-dAMT, 2-desamino-AMT;2-CH3-AMT, 2-desamino-2-methyl-AMT; 10-EdAM,10-ethyl-10-deazaaminopterin; PT523,Nα-(4-amino-4-deoxypteroyl)-Nδ-(hemiphthaloyl)-L-ornithine; DDATHF,5,10-dideaza-5,6,7,8,-tetrahydrofolic acid; 5-d(i)H4PteGlu,5-deaza-5,6,7,8-tetrahydroisofolic acid; N9-CH3-5-d(i)H4PteGlu,N9-methyl-5-deaza-5,6,7,8-tetrahydroisofolic acid; 5-dPteHCysA,Nα-(5-deazapteroyl)-L-homocysteic acid; 5-dPteAPBA,Nα-(5-deazapteroyl)-DL-2-amino-4-phosphonobutanoic acid; 5-dPteOrn,Nα-(5-deazapteroyl)-L-ornithine; 5-dH4PteHCysA,Nα-(5-deaza-5,6,7,8-tetrahydropteroyl)-L-homocysteic acid; 5-dH4PteAPBA,Nα-(5-deaza-5,6,7,8-tetrahydropteroyl)-DL-2-amino-4-phosphobutanoicacid; 5-dH4PteOro, Nα-(5-deaza-5,6,7,8-tetrahydropteroyl)-L-ornithine;CB3717, N10-propargyl-5,8-dideazafolic acid; ICI-198,583,2-desamino-2-methyl-N10-propargyl-5,8-dideazafolic acid;4-H-ICI-198,583, 4-deoxy-ICI-198,583: 4-OCH3-ICI-198,583,4-methoxy-ICI-198,583 Glu-to-Val-ICI-198,583; valine-ICI-198;583;Glu-to-Sub-ICI-198,583, 2-amino-suberate-ICI-198,583; 7-CH3-ICI-198,583,7-methyl-ICI-198,583; ZD1694,N-[5(N-(3,4-dihydro-2-methyl-4-oxoquinazolin-6-yl-methyl)amino)2-thienyl)]-L-glutamicacid; 2-NH2-ZD1694, 2-amino-ZD1694; BW1843U89,(S)-2[5-(((1,2-dihydro-3-methyl-1-oxobenzo(f)quinazolin-9-yl)methyl)amino)-1-oxo-2-isoindolinyl]-glutaricacid; LY231514,N-(4-(2-(2-amino-4,7-dihydro-4-oxo-3H-pyrrolo[2,3-D]pyrimidin-5-yl)ethyl)benzoyl]-L-glutamicacid; IAHQ, 5,8-dideazaisofolic acid; 2-dIAHQ, 2-desamino-IAHQ;2-CH3-dIAHQ, 2-desamino-2-methyl-IAHQ; 5-d(i)PteGlu, 5-deazaaisofolicacid; N9-CH3-5-d(i)PteGlu, N9-methyl-5-deazaisofolic acid;N9-CHO-5-d(i)PteGlu, N9-formyl-5-deazaisofolic acid; AG337,3,4-dihydro-2-amino-6-methly-4-oxo-5-(4-pyridylthio)quanazoline; andAG377, 2,4-diamino-6[N-(4-(phenysulfonyl)benzyl)ethyl)amino]quinazoline.

In another embodiment the folate receptor binding antifolate is selectedfrom aminopterin, methotrexate, raltitrexed (also referred to asTOMUDEX, ZD1694), plevitrexed (also referred to as BGC 9331; ZD9331),pemetrexed (also referred to as ALIMTA, LY231514), lometrexol(5,10-dideazatetrahydrofolic acid) and related cyclopenta[g]quinazolineswith dipeptide ligands, CB3717, CB300945 (also referred to as BGC945)and stereoisomers thereof such as 6-R,S-BGC 945, CB300638 (also referredto as BGC638), and BW1843U89. The preparation of illustrativeantifolates are described in Bavetsias et al., 2000; Bavetsias et al.,2002; Gibbs et al., 2005; Henderson et al., 2006; Jackman et al., 2004;and Theti et al., 2003. The foregoing publications, and each additionalpublication cited herein is incorporated herein by reference. In anotherembodiment, the folate receptor binding antifolate is selected fromaminopterin, methotrexate, CB3717, plevitrexed, raltitrexed, BGC 945,pemetrexed, and the like. In another embodiment, the antifolate isselected from CB3717, plevitrexed, raltitrexed, and 5-Me-THF. In anotherembodiment, the antifolate is selected from BGC945, BGC 638, andBGC9331.

In another embodiment, the antifolate is a compound having a relativeaffinity for the folate receptor of about 0.1 or greater at atemperature of about 20° C. or greater. In another embodiment, theantifolate is selected from 2-CH3-dIAHQ, 5-dPteAPBA, 5-dPteOrn,N9-CHO-5-d(i)PteGlu, 2-dIAHQ, 7-CH3-ICI-198583, GLu-to-Val-ICI-198583,Glu-to-Sub-ICI-198583, 4-MeO-ICI-198583, ICI-198583, 5-dH4PteHCysA,N9-CH3-5-d(i)H4PteGlu, 5-d(i)H4PteGlu, 5-CH3-THF, N9-CH3-5-d(i)PteGlu,5-d(i)PteGlu, IAHQ, LY231514, BW1843U89, 2-NH-2-ZD1694, ZD1694, CB3717,5-dH4PteOrn, 5-dH4PteAPBA, 5-dPteHCysA, and DDATHF.

In another embodiment, the antifolate is a compound having a relativeaffinity for the folate receptor of about 0.2 or greater at atemperature of about 20° C. or greater. In another embodiment, theantifolate is selected from N9-CHO-5-d(i)PteGlu, 2-dIAHQ,7-CH3-ICI-198583, Glu-to-Val-ICI-198583,Glu-to-Sub-ICI-198583,4-MeO-ICI-198583, ICI-198583, 5-dH4PteHCysA, N9-CH-3-5-d(i)H4PteGlu,5-d(i)H4PteGlu, 5-CH3-THF, N9-CH3-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ,LY231514, BW1843U89, 2-NH2-ZD1694, ZD1694, CB3717, 5-dH4PteOrn,5-dH4PteAPBA, 5-dPteHCysA, and DDATHF.

In another embodiment, the antifolate is a compound having a relativeaffinity for the folate receptor of about 0.5 or greater at atemperature of about 20° C. or greater. In another embodiment, theantifolate is selected from N9-CH3-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ,LY231514, BW1843U89, 2-NH2-ZD1694, ZD1694, CB3717, 5-dH4PteOrn,5-dH4PteAPBA, 5-dPteHCysA, and DDATHF.

In another embodiment, the antifolate is selected from 5-dPteAPBA,5-dPteOrn, and 2-CH3-IAHQ. In another embodiment, the antifolate isselected from 5-d(i)H4PteGlu, N9-CH3-5-d(i)H4PteGlu, ICI-198583,4-MeO-ICI-198583, Glu-to-Val-ICI-198583, Glu-to-Sub-ICI-198583,7-CH3-ICI-198583, N9-CHO-5-d(i)PteGlu, and 2d-IAHQ. In anotherembodiment, the antifolate is selected from 5-d(i)PteGlu,N9-CH3-5-d(i)PteGlu, pemetrexed, CB3717. ralitrexed,2-desmethyl-2-NH2-ralitrexed, BW 1834U89, IAHQ, 5-dH4PteHCysA,dH4PteAPBA, dH4PteOrn, and DDATHF.

In another embodiment, the antifolate is a deaza or dideaza analog offolate, including reduced derivatives thereof. In another embodiment,the antifolate is CB3717, In another embodiment, the antifolate is5-Me-THF.

Alternatively, in another embodiment, the antifolate is not leucovorin.Alternatively, in another embodiment, the antifolate is not pteroicacid. Alternatively, in another embodiment, the antifolate is notpemetrexed. Alternatively, in another embodiment, the antifolate is notmethotrexate.

In another embodiment, the antifolate is a compound of the formula:

wherein X═PO(OH)₂ (5-dPteAPBA), CH₂NH₂ (5-dPteOrn), or SO₂OH(5-dPteHCysA).

In another embodiment, the antifolate is a compound of the formula:

wherein X═N, Y═NH₂, R═H (5-d(i)PteGlu), X═N, Y═NH₂, R═CH₃(N⁹—CH₃-5-d(i)PteGlu), X═N, Y═NH₂, R═CHO (N⁹—CHO-5-d(i)PteGlu), X═CH,Y═NH₂, R═H (IAHQ) X═CH, Y═H, R═H (2-dIAHQ), or X═CH, Y═CH₃, R═H(2-CH₃-dIAHQ).

In another embodiment, the antifolate is a compound of the formula:

wherein X═OH, R═H, Y=Glu (ICI-198583), X═OCH₃, R═H, Y=Glu(4-MeO-ICI-198583), X═OH, R═H, Y=Valine (Glu-to-Val-ICI-198583), X═OH,R═H, Y=Suberate (Glu-Sub-ICI-198583), or X═OH, R═CH₃, Y=Glu(7-CH₃-ICI-198583).

In another embodiment, the antifolate is a compound of the formula:

wherein X═PO(OH)₂ (5-dH₄PteAPBA), CH₂NH₂ (5-dH₄PteOrn), or SO₂OH(5-dH₄PteHCysA).

In another embodiment, the antifolate is a compound of the formula:

wherein A=NH (5-d(i)H₄PteGlu), NCH₃ (N⁹—CH3-5-d(i)H₄PteGlu), or CH₂(DDATHF).

In another embodiment, the antlfolate is a BW 1834U89, of the followingformula:

In another embodiment, the antifolate is BCC 945 (R═CH₂OH) or BGC 638(R═CH₃) of the following formula.

In one variation, the absolute stereochemistry of these antifoiates isL-Glu-D-Glu,

In another embodiment, the antifolate is a compound of the formula:

Additional antifolates are described in Gangiee et al., J Med Chem10.1021/jm800244v (2008), the disclosiure of which is incpripratedherein by reference.

In another embodiment, in each of the foregoing compounds that includesa glutamate radical, the corresponding analogs are also described hereinwhere one or more amino acids, as described herein, replaces theglutamate. It is to be understood that such amino acids replacingglutamate may be naturally occurring, such as Asp, Cys, Ser, Thr, Lys,and the like, or may be unnatural, including but not limited tounnatural absolute configurations, beta amino acids, unnatural sidechains, and the like. In another embodiment, at least one of the aminoacids replacing glutamate is charged. In another embodiment, Glu isreplaced by the dipeptide (L-Glu-γ-D-Glu) moiety.

The drug can be any molecule capable of modulating or otherwisemodifying cell function, including pharmaceutically active compounds.Suitable molecules can include, but are not limited to: peptides,oligopeptides, retro-inverso oligopeptides, proteins, protein analogs inwhich at least one non-peptide linkage replaces a peptide linkage,apoproteins, glycoproteins, enzymes, coenzymes, enzyme inhibitors, aminoacids and their derivatives, receptors and other membrane proteins;antigens and antibodies thereto; haptens and antibodies thereto;hormones, lipids, phospholipids, liposomes; toxins; antibiotics;analgesics; bronchodilators; beta-blockers; antimicrobial agents;antihypertensive agents; cardiovascular agents includingantiarrhythmics, cardiac glycosides, antianginals and vasodilators;central nervous system agents including stimulants, psychotropics,antimanics, and depressants; antiviral agents; antihistamines; cancerdrugs including chemotherapeutic agents; tranquilizers;anti-depressants; H-2 antagonists; anticonvulsants; antinauseants;prostaglandins and prostaglandin analogs; muscle relaxants: stimulants;decongestants; antiemetics; diuretics; antispasmodics antiasthmatics;anti-Parkinson agents; expectorants; cough suppressants; and mucolytics.

Further, the drug can be any drug known in the art which is cytotoxic,enhances tumor permeability, inhibits tumor cell proliferation, promotesapoptosis, decreases anti-apoptotic activity in target cells, is used totreat diseases caused by infectious agents, or is useful for treating adisease state caused by any type of pathogenic cell. Drugs suitable foruse in accordance with this invention include alkylating agents,antiandrogens, antiestrogens, androgens, aclamycin and aclamycinderivatives, estrogens, antimetabolites such as cytosine arabinoside,purine analogs, pyrimidine analogs, busulfan, carboplatin, chlorambucil,cisplatin and other platinum compounds, tamoxiphen, taxol, paclitaxel,paclitaxel derivatives, Taxotere®, cyclophosphamide, daunomycin,rhizoxin, T2 toxin, plant alkaloids, prednisone, hydroxyurea,teniposide, mitomycins, discodermolides, microtubule inhibitors,epothilones, tubulysin, cyclopropyl benz[e] indolone, seco-cyclopropylbenz[e] indolone, O-Ac-seco-cyclopropyl benz[e] indolone, bleomycin andany other antibiotic, nitrogen mustards, nitrosureas, vincristine,vinblastine, analogs and derivative thereof such as deacetylvinblastinemonohydrazide, and other vinca alkaloids, including those described inPCT international publication No. WO 2007/022493, the disclosure ofwhich is incorporated herein by reference, colchicine, colchicinederivatives, allocolchicine, thiocolchicine, trityl cysteine,Halicondrin B, dolastatins such as dolastatin 10, amanitins such asα-amanitin, camptothecin, irinotecan, and other camptothecin derivativesthereof, maytansines, geldanamycin and geldanamycin derivatives,estramustine, nocodazole, MAP4, colcemid, peptide and peptidomimeticsignal transduction inhibitors, and any other drug or toxin. Other drugsthat can be used in accordance with the invention include penicillins,cephalosporins, vancomycin, erythromycin, clindamycin, rifampin,chloramphenicol, aminoglycoside antibiotics, gentamicin, amphotericin B,acyclovir, trifluridine, ganciclovir, zidovudine, amantadine, ribavirin,and any other antimicrobial compound.

In another embodiment, the drug is a vinca alkaloid, including but notlimited to vinblastine, vincristine, vindesine, and the like, andanalogs and derivatives thereof. In another embodiment, the drug is atubulysin, and analogs and derivatives thereof. In another embodiment,the drug is a epothilone, and analogs and derivatives thereof. Inanother embodiment, the drug is a mitomycin, and analogs and derivativesthereof. In one selection of each of the foregoing embodiments, theantifolate is EC282.

In another embodiment, processes for preparing the compounds aredescribed herein. Illustratively, EC0284 is prepared as follows:

Although illustrated for EC0284, it is to be understood that theforegoing illustrative synthesis may be routinely modified and adaptedto prepare other compounds described herein by the appropriate selectionof starting materials.

The monovalent or multivalent linker is any chain of atoms having two ormore points of attachment for connecting the antifolate that the one ormore drugs, and which may be linear, branched, or cyclic, oralternatively include one or more cyclic regions. Illustratively, thelinker comprises C, N, O, P, S, and Si. The monovalent or multivalentlinker also includes at least one releasable linker.

The term “releasable linker” as used herein generally refers to a linkerthat includes at least one bond that can be broken under physiologicalconditions (e.g., a pH-labile, acid-labile, oxidatively-labile, and/orenzyme-labile bond). It should be appreciated that such physiologicalconditions resulting in bond breaking include standard chemicalhydrolysis reactions that occur, for example, at physiological pH, or asa result of compartmentalization into a cellular organelle such as anendosome having a lower pH than cytosolic pH. In one variation, thephysiological conditions are those found in an endosome.

The cleavable bond or bonds may be present in the interior of acleavable linker and/or at one or both ends of a cleavable linker. Inother words, the releasable linker may contain the scissile bond or maybe connected to another linker, such as a spacer linker, oralternatively to a drug or the antifolate via the scissile bond. It isappreciated that the lability of the cleavable bond may be adjusted byincluding functional groups or fragments within the linker L that areable to assist or facilitate such bond breakage, also termed anchimericassistance. In addition, it is appreciated that additional functionalgroups or fragments may be included within the polyvalent linker L thatare able to assist or facilitate additional fragmentation of thereceptor binding ligand agent conjugates after bond breaking of thereleasable linker. The lability of the cleavable bond can be adjustedby, for example, substitutional changes at or near the cleavable bond,such as including alpha branching adjacent to a cleavable disulfidebond, increasing the hydrophobicity of substituents on silicon in amoiety having a silicon-oxygen bond that may be hydrolyzed, homologatingalkoxy groups that form part of a ketal or acetal that may behydrolyzed, and the like. It is also to be understood that such linkerscontain more than one releasable linker. For example, self-immolativelinkers are described herein that contain more than one releasablelinker.

Accordingly, it is to be understood that a cleavable bond can connecttwo adjacent atoms within the releasable linker and/or connect otherlinkers or A and/or D, as described herein, at either or both ends ofthe releasable linker. In the case where a cleavable bond connects twoadjacent atoms within the releasable linker, following breakage of thebond, the releasable linker is broken into two or more fragments.Alternatively, in the case where a cleavable bond is between thereleasable linker and another moiety, such as an additional heteroatom,additional spacer linker, another releasable linker, the antifolate A,or a drug D, following breakage of the bond, the releasable linker isseparated from the other moiety.

In another embodiment, the linker L, includes a disulfide releasablelinker. In another embodiment, the linker L includes at least onereleasable linker that is not a disulfide releasable linker. In anotherembodiment, the linker L includes at least two releasable linkers. Inanother embodiment, the linker L includes at least two releasablelinkers, where at least one releasable linker is not a disulfidereleasable linker. In another embodiment, the linker L includes at leasttwo releasable linkers, where at least one releasable linker isseparates each drug D from the antifolate.

In another embodiment, the releasable and spacer linkers may be arrangedin such a way that subsequent to the cleavage of a bond in the bivalentlinker, released functional groups chemically assist the breakage orcleavage of additional bonds, also termed anchimeric assisted cleavageor breakage. It is to be understood that such releasable linkers containat least two releasable linkers. An illustrative embodiment of such abivalent linker or portion thereof includes compounds having theformulae:

where X is an heteroatom, such as nitrogen, oxygen, or sulfur, or acarbonyl group; n is an integer selected from 0 to 4; illustratively 2;R is hydrogen, or a substituent, including a substituent capable ofstabilizing a positive charge inductively or by resonance on the arylring, such as alkoxy and the like, including methoxy; and the symbol (*)indicates points of attachment for additional spacer, heteroatom, orreleasable linkers forming the bivalent linker, or alternatively forattachment of the drug, or analog or derivative thereof, or theantifolate, or analog or derivative thereof. In one embodiment, n is 2and R is methoxy. It is appreciated that other substituents may bepresent on the aryl ring, the benzyl carbon, the alkanoic acid, or themethylene bridge, including but not limited to hydroxy, alkyl, alkoxy,alkylthio, halo, and the like. Assisted cleavage may include mechanismsinvolving benzylium intermediates, benzyne intermediates, lactonecyclization, oxonium intermediates, beta-elimination, and the like. Itis further appreciated that, in addition to fragmentation subsequent tocleavage of the releasable linker, the initial cleavage of thereleasable linker may be facilitated by an anchimerically assistedmechanism.

Illustrative mechanisms for cleavage of the bivalant linkers describedherein include the following 1,4 and 1,6 fragmentation mechanisms

where X is an exogenous or endogenous nucleophile, glutathione, orbioreducing agent, and the like, and either of Z or Z′ is theantifolate, or the drug, or am antifolate or drug moiety in conjunctionwith other portions of the polyvalent linker. It is to be understoodthat although the above fragmentation mechanisms are depicted asconcerted mechanisms, any number of discrete steps may take place toeffect the ultimate fragmentation of the polyvalent linker to the finalproducts shown. For example, it is appreciated that the bond cleavagemay also occur by acid-catalyzed elimination of the carbamate moiety,which may be anchimerically assisted by the stabilization provided byeither the aryl group of the beta sulfur or disulfide illustrated in theabove examples. In those variations of this embodiment, the releasablelinker is the carbamate moiety. Alternatively, the fragmentation may beinitiated by a nucleophilic attack on the disulfide group, causingcleavage to form a thiolate. The thiolate may intermolecularly displacea carbonic acid or carbamic acid moiety and form the correspondingthiacyclopropane. In the case of the benzyl-containing polyvalentlinkers, following an illustrative breaking of the disulfide bond, the,resulting phenyl thiolate may farther fragment to release a carbonicacid or carbamic acid moiety by forming a resonance stabilizedintermediate. In any of these cases, the releasable nature of theillustrative polyvalent linkers described herein may be realized bywhatever mechanism may be relevant to the chemical, metabolic,physiological, or biological conditions present.

Other illustrative mechanisms for bond cleavage of the releasable linkerinclude oxonium-assisted cleavage as follows;

where Z is the antifolate, or the drug, or each is an antifolate or drugmoiety in conjunction with other portions of the polyvalent linker, suchas a drug or antifolate moiety including one or more spacer linkersand/or other releasable linkers. Without being bound by theory, in thisembodiment, acid catalysis, such as in an endosome, may initiate thecleavage via protonation of the urethane group. In addition,acid-catalyzed elimination of the carbamate leads to the release of CO₂and the nitrogen-containing moiety attached to Z, and the formation of abenzyl cation, which may be trapped by water, or any other Lewis base.

Other illustrative linkers include compounds of the formulae:

where X is NH, CH₂, or O; R is hydrogen, or a substituent, including asubstituent capable of stabilizing a positive charge inductively or byresonance on the aryl ring, such as alkoxy and the like, includingmethoxy; and the symbol (*) indicates points of attachment foradditional spacer, heteroatom, or releasable linkers forming thebivalent linker, or alternatively for attachment of the drug, or theantifolate.

Illustrative mechanisms for cleavage of such bivalent linkers describedherein include the following 1,4 and 1,6 fragmentation mechanismsfollowed by anchimerically assisted cleavage of the acylated Z′ viacyclization by the hydrazide group:

where X is an exogenous or endogenous nucleophile, glutathione, orbioreducing agent, and the like, and either of Z or Z′ is theantifolate, or the drug, or an antifolate or drug moiety in conjunctionwith other portions of the polyvalent linker. It is to be understoodthat although the above fragmentation mechanisms are depicted asconcerted mechanisms, any number of discrete steps may take place toeffect the ultimate fragmentation of the polyvalent linker to the finalproducts shown. For example, it is appreciated that the bond cleavagemay also occur by acid-catalyzed elimination of the carbamate moiety,which may be anchimerically assisted by the stabilization provided byeither the aryl group of the beta sulfur or disulfide illustrated in theabove examples. In those variations of this embodiment, the releasablelinker is the carbamate moiety. Alternatively, the fragmentation may beinitiated by a nucleophilic attack on the disulfide group, causingcleavage to form a thiolate. The thiolate may intermolecularly displacea carbonic acid or carbamic acid moiety and form the correspondingthiacyclopropane. In the case of the benzyl-containing polyvalentlinkers, following an illustrative breaking of the disulfide bond, theresulting phenyl thiolate may further fragment to release a carbonicacid or carbarnic acid moiety by forming a resonance stabilizedintermediate. In any of these cases, the releasable nature of theillustrative polyvalent linkers described herein may be realized bywhatever mechanism may be relevant to the chemical, metabolic,physiological, or biological conditions present. Without being bound bytheory, in this embodiment, acid catalysis, such as in an endosome, mayalso initiate the cleavage via protonation of the urethane group. Inaddition, acid-catalyzed elimination of the carbamate leads to therelease of CO₂ and the nitrogen-containing moiety attached to Z, and theformation of a benzyl cation, which may be trapped by water, or anyother Lewis base, as is similarly described herein.

In another embodiment, the polyvalent linkers described herein arecompounds of the following formulae

where n is an integer selected from 1 to about 4; R^(a) and R^(h) areeach independently selected from the group consisting of hydrogen andalkyl, including lower alkyl such as C₁-C₄ alkyl that are optionallybranched; or R^(a) and R^(b) are taken together with the attached carbonatom to form a carbocyclic ring; R is an optionally substituted alkylgroup, an optionally substituted acyl group, or a suitably selectednitrogen protecting group; and (*) indicates points of attachment forthe drug, or antifolate, other polyvalent linkers, or other parts of theconjugate.

In another embodiment, the polyvalent linkers described herein includecompounds of the following formulae

where m is an integer selected from 1 to about 4; R is an optionallysubstituted alkyl group, an optionally substituted acyl group, or asuitably selected nitrogen protecting group; and (*) indicates points ofattachment for the drug, antifolate, other polyvalent linkers, or otherparts of the conjugate.

In another embodiment, the polyvalent linkers described herein includecompounds of the following formulae

where in is an integer selected from 1 to about 4; R is an optionallysubstituted alkyl group, an optionally substituted acyl group, or asuitably selected nitrogen protecting group; and (*) indicates points ofattachment for the drug, antifolate, other polyvalent linkers, or otherparts of the conjugate.

Another illustrative mechanism involves an arrangement of the releasableand spacer linkers in such a way that subsequent to the cleavage of abond in the bivalent linker, released functional groups chemicallyassist the breakage or cleavage of additional bonds, also termedanchimeric assisted cleavage or breakage. An illustrative embodiment ofsuch a bivalent linker or portion thereof includes compounds having theformula:

where X is an heteroatom, such as nitrogen, oxygen, or sulfur, n is aninteger selected from 0, 1, 2, and 3, R is hydrogen, or a substituent,including a substituent capable of stabilizing a positive chargeinductively or by resonance on the aryl ring, such as alkoxy, and thelike, and either of Z or Z′ is the antifolate, or the drug, or anantifolate or drug moiety in conjunction with other portions of thebivalent linker. It is appreciated that other substituents may bepresent on the aryl ring, the benzyl carbon, the carbamate nitrogen, thealkanoic acid, or the methylene bridge, including but not limited tohydroxy, alkyl, alkoxy, alkylthio, halo, and the like. Assisted cleavagemay include mechanisms involving benzylium intermediates, benzyneintermediates, lactone cyclization, oxonium intermediates,beta-elimination, and the like. It is further appreciated that, inaddition to fragementation subsequent to cleavage of the releasablelinker, the initial cleavage of the releasable linker may be facilitatedby an anchimerically assisted mechanism.

In this embodiment, the hydroxyalkanoic acid, which may cyclize,facilitates cleavage of the methylene bridge, by for example an oxoniumion, and facilitates bond cleavage or subsequent fragmentation afterbond cleavage of the releasable linker. Alternatively, acid catalyzedoxonium ion-assisted cleavage of the methylene bridge may begin acascade of fragmentation of this illustrative bivalent linker, orfragment thereof. Alternatively, acid-catalyzed hydrolysis of thecarbamate may facilitate the beta elimination of the hydroxyalkanoicacid, which may cyclize, and facilitate cleavage of methylene bridge, byfor example an oxonium ion. It is appreciated that other chemicalmechanisms of bond breakage or cleavage under the metabolic,physiological, or cellular conditions described herein may initiate sucha cascade of fragmentation. It is appreciated that other chemicalmechanisms of bond breakage or cleavage under the metabolic,physiological, or cellular conditions described herein may initiate sucha cascade of fragmentation.

In another embodiment, the releasable and spacer linkers may be arrangedin such a way that subsequent to the cleavage of a bond in thepolyvalent linker, released functional groups chemically assist thebreakage or cleavage of additional bonds, also termed anchimericassisted cleavage or breakage. An illustrative embodiment of such apolyvalent linker or portion thereof includes compounds having theformula:

where X is an heteroatom, such as nitrogen, oxygen, or sulfur, n is aninteger selected from 0, 1, 2, and 3, R is hydrogen, or a substituent,including a substituent capable of stabilizing a positive chargeinductively or by resonance on the aryl ring, such as alkoxy, and thelike, and the symbol (*) indicates points of attachment for additionalspacer, heteroatom, or releasable linkers forming the polyvalent linker,or alternatively for attachment of the drug, or the antifolate. It isappreciated that other substituents may be present on the aryl ring, thebenzyl carbon, the alkanoic acid, or the methylene bridge, including butnot limited to hydroxy, alkyl, alkoxy, alkylthio, halo, and the like.Assisted cleavage may include mechanisms involving benzyliumintermediates, benzyne intermediates, lactone cyclization, oxoniumintermediates, beta-elimination, and the like. It is further appreciatedthat, in addition to fragmentation subsequent to cleavage of thereleasable linker, the initial cleavage of the releasable linker may befacilitated by an anchimerically assisted mechanism.

Another illustrative embodiment of the linkers described herein, includereleasable linkers that cleave under the conditions described herein bya chemical mechanism involving beta elimination. In one aspect, suchreleasable linkers include beta-thio, beta-hydroxy, and, beta-aminosubstituted carboxylic acids and derivatives thereof, such as esters,amides, carbonates, carbamates, and ureas. In another aspect, suchreleasable linkers include 2-and 4-thioarylesters, carbamates, andcarbonates.

In another illustrative embodiment, the linker includes one or moreamino acids. In one variation, the linker includes a single amino acid.In another variation, the linker includes a peptide having from 2 toabout 50, 2 to about 30, or 2 to about 20 amino acids. In anothervariation, the linker includes a peptide having from about 4 to about 8amino acids. Such amino acids are illustratively selected from thenaturally occurring amino acids, or stereoisomers thereof. The aminoacid may also be any other amino acid, such as any amino acid having thegeneral formula:—N(R)—(CR′R″)_(q)—C(O)—where R is hydrogen, alkyl, acyl, or a suitable nitrogen protectinggroup, R′ and R″ are hydrogen or a substituent, each of which isindependently selected in each occurrence, and q is an integer such as1, 2, 3, 4, or 5. Illustratively, R′ and/or R″ independently correspondto, but are not limited to, hydrogen or the side chains present onnaturally occurring amino acids, such as methyl, benzyl, hydroxymethyl,thiomethyl, carboxyl, carboxylmethyl, guanidinopropyl, and the like, andderivatives and protected derivatives thereof. In another embodiment, R′and/or R″ independently correspond to, but are not limited to, hydrogenor analogs of the side chains present on naturally occurring aminoacids, such as the corresponding amino analogs of serine and threonine,such as beta-aminoalanine. The above described formula includes allstereoisomeric variations. For example, the amino acid may be selectedfrom asparagine, aspartic acid, cysteine, glutamic acid, lysine,glutamine, arginine, serine, ornitine, threonine, and the like. In onevariation, the releasable linker includes at least 2 amino acidsselected from asparagine, aspartic acid, cysteine, glutamic acid,lysine, glutamine, arginine, serine, ornitine, and threonine. In anothervariation, the releasable linker includes between 2 and about 5 aminoacids selected from asparagine, aspartic acid, cysteine, glutamic acid,lysine, glutamine, arginine, serine, ornitine, and threonine. In anothervariation, the releasable linker includes a tripeptide, tetrapeptide,pentapeptide, or hexapeptide consisting of amino acids selected fromaspartic acid, cysteine, glutamic acid, lysine, arginine, and ornitine,and combinations thereof.

The term amino acid as used herein refers generally toaminoalkylcarboxylate, where the alkyl radical is optionallysubstituted, such as with alkyl, hydroxy sulfhydrylalkyl, aminoalkyl,carboxyalkyl, and the like, including groups corresponding to thenaturally occurring amino acids, such as serine, cysteine, methionine,aspartic acid, glutamic acid, and the like. It is to be understood thatsuch amino acids may be of a single stereochemistry or a particularmixture of stereochemisties, including racemic mixtures. In addition,amino acid refers to beta, such as beta alanine, and the like, gamma,and longer amino acids, such as amino acids of the formula:—N(R)—(CR′R″)_(q)—C(O)—where R is hydrogen, alkyl, acyl, or a suitable nitrogen protectinggroup, R′ and R″ are hydrogen or a substituent, each of which isindependently selected in each occurrence, and q is an integer such as1, 2, 3, 4, or 5Illustratively, R′ and/or R″ independently correspondto, but are not limited to, hydrogen or the side chains present onnaturally occurring amino acids, such as methyl, benzyl, hydroxymethyl,thiomethyl, carboxyl, carboxyimethyl, guanidinopropyl, and the like, andderivatives and protected derivatives thereof. The above describedformula includes all stereoisomeric variations. For example, the aminoacid may be selected from asparagine, aspartic acid, cysteine, glutamicacid, lysine, glutamine, arginine, serine, omitine, threonine, and thelike. In another illustrative aspect of the vitamin receptor bindingdrug delivery conjugate intermediate described herein, the drug, or ananalog or a derivative thereof, includes an alkylthiol nucleophile.

Additional examples of linkers, such as additional multivalent linkers,hydrophilic linkers, and the like are described in U.S. PatentApplication Publication No. 2005/0002942, U.S. Patent ApplicationPublication No. 2008/0248052, U.S. Patent Application Publication Ser.No. 2008/056824, and PCT International Application Publication No. WO2009/002993, the disclosures of which are incorporated herein byreference in their entirety.

In another embodiment, a pharmaceutical composition comprising any oneof the preceding targeted delivery conjugates and one or more carriers,excipients, diluents, and combinations thereof is described.

In another embodiment, a method is described for treating a pathogenicpopulation of cells in a patient, the method comprising the step ofadministering an effective amount of any one of the preceding targeteddelivery conjugates.

In another embodiment, a method for treating a patient in need of reliefof a disease is described, the method comprising the step ofadministering an therapeutically effective amount of any one of thepreceding targeted delivery conjugates to the patient. In one embodimentthe disease is cancer.

The antifolate drug delivery conjugates described herein can be used forboth human clinical medicine and veterinary applications. Thus, the hostanimal harboring the population of pathogenic cells and treated with thedrug delivery conjugates can be human or, in the case of veterinaryapplications, can be a laboratory, agricultural, domestic, or wildanimal. The methods described herein can be applied to host animalsincluding, but not limited to, humans, laboratory animals such rodents(e.g., mice, rats, hamsters, etc,), rabbits, monkeys, chimpanzees,domestic animals such as dogs, cats, and rabbits, agricultural animalssuch as cows, horses, pigs, sheep, goats, and wild animals in captivitysuch as hears, pandas, lions, tigers, leopards, elephants, zebras,giraffes, gorillas, dolphins, and whales.

The methods are applicable to populations of pathogenic cells that causea variety of pathologies in these host animals. The term pathogeniccells refers to for example cancer cells, infectious agents such asbacteria and viruses, bacteria-or virus-infected cells, and any othertype of pathogenic cells that uniquely express, preferentially express,or over-express folate receptors. Pathogenic cells can also include anycells causing a disease state for which treatment with the antifolatedrug delivery conjugates described herein results in reduction of thesymptoms of the disease.

In another embodiment, the population of pathogenic cells can be acancer cell population that is tumorigenic, including benign tumors andmalignant tumors, or it can be non-tumorigenic. The cancer cellpopulation can arise spontaneously or by such processes as mutationspresent in the germline of the host animal or somatic mutations, or itcan be chemically-, virally-, or radiation-induced. The methods can beutilized to treat such cancers as carcinomas, sarcomas, lymphomas,Hodgkin's disease, melanomas, mesotheliomas, Burkitt's lymphoma,nasopharyngeal carcinomas, leukemias, and myelomas. The cancer cellpopulation can include, but is not limited to, oral, thyroid, endocrine,skin, gastric, esophageal, laryngeal, pancreatic, colon, bladder, bone,ovarian, cervical, uterine, breast, testicular, prostate, rectal,kidney, liver, and lung cancers.

In embodiments where the pathogenic cell population is a cancer cellpopulation, the effect of conjugate administration is a therapeuticresponse measured by reduction or elimination of tumor mass or ofinhibition of tumor cell proliferation. In the case of a tumor, theelimination can be an elimination of cells of the primary tumor or ofcells that have metastasized or are in the process of dissociating fromthe primary tumor. A prophylactic treatment with the drug deliveryconjugate to prevent return of a tumor after its removal by anytherapeutic approach including surgical removal of the tumor, radiationtherapy, chemotherapy, or biological therapy is also described. Theprophylactic treatment can be an initial treatment with the drugdelivery conjugate, such as treatment in a multiple dose daily regimen,and/or can be an additional treatment or series of treatments after aninterval of days or months following the initial treatment(s).Accordingly, elimination of any of the pathogenic cell populationstreated using the described methods includes reduction in the number ofpathogenic cells, inhibition of proliferation of pathogenic cells, aprophylactic treatment that prevents return of pathogenic cells, or atreatment of pathogenic cells that results in reduction of the symptomsof disease.

In cases where cancer cells are being eliminated, the methods can beused in combination with surgical removal of a tumor, radiation therapy,chemotherapy, or biological therapies such as other immunotherapiesincluding, but not limited to, monoclonal antibody therapy, treatmentwith immunomodulatory agents, adoptive transfer of immune effectorcells, treatment with hematopoletic growth factors, cytokines andvaccination.

In one embodiment, the antifolate drug delivery conjugates can beinternalized into the targeted pathogenic cells upon binding of theantifolate moiety to a receptor, transporter, or other surface-presentedprotein that specifically binds the ligand and which is preferentiallyexpressed on the pathogenic cells. Such internalization can occur, forexample, through receptor-mediated endocytosis. Antifolate drug deliveryconjugates containing one or more releasable linkers allow the bindingligand moiety and the drug to dissociate intracelhalarly and the drugcan act on its intracellular target.

Generally, any manner of forming a conjugate between the bivalent linker(L) and the antifolate, or analog or derivative thereof, between thebivalent linker (L) and the drug, or analog or derivative thereof,including any intervening heteroatom, can be utilized. Also, anyart-recognized method of forming a conjugate between the spacer linker,the releasable linker, and the any additional heteroatoms to form thelinker L can be used. Covalent bonding can occur, for example, throughthe formation of amide, ester, disulfide, or imino bonds between acid,aldehyde, hydroxy, amino, sulthydryl, or hydrazo groups present on anyof the linkers, drugs, and/or antifolates.

In another illustrative aspect, any effective regimen for administeringthe antifolate drug delivery conjugates can be used. For example, theantifolate drug delivery conjugates can be administered as single doses,or can be divided and administered as a multiple-dose daily regimen. Inother embodiments, a staggered regimen, for example, one to three daysper week can be used as an alternative to daily treatment, and suchintermittent or staggered daily regimen is considered to be equivalentto every day treatment and within the scope of the methods describedherein. In one embodiment, the host is treated with multiple injectionsof the antifolate drug delivery conjugate to eliminate the population ofpathogenic cells. In another embodiment, the host is injected multipletimes (preferably about 2 up to about 50 times) with the antifolate drugdelivery conjugate, for example, at 12-72 hour intervals or at 48-72hour intervals. In other embodiments, additional injections of theantifolate drug delivery conjugate can be administered to the patient atan interval of days or months after the initial injections(s) and theadditional injections prevent recurrence of the disease state caused bythe pathogenic cells.

In another embodiment, pharmaceutical compositions comprising an amountof a antifolate drug delivery conjugate effective to eliminate apopulation of pathogenic cells in a host animal when administered in oneor more doses are described. The antifolate drug delivery conjugate ispreferably administered to the host animal parenterally, e.g.,intradermally, subcutaneously, intramuscularly, intraperitoneally,intravenously, or intrathecaliy. Alternatively, the antifolate drugdelivery conjugate can be administered to the host animal by othermedically useful processes, such as orally, and any effective dose andsuitable therapeutic dosage form, including prolonged release dosageforms, can be used.

Examples of parenteral dosage forms include aqueous solutions of theactive agent, in an isotonic saline, 5% glucose or other well-knownpharmaceutically acceptable liquid carriers such as liquid alcohols,glycols, esters, and amides. The parenteral dosage form can be in theform of a reconstitutable lyophilizate comprising the dose of the drugdelivery conjugate. In one aspect of the present embodiment, any of anumber of prolonged release dosage forms known in the art can beadministered such as, for example, the biodegradable carbohydratematrices described in U.S. Pat. Nos. 4,713,249; 5,266,333; and5,417,982, the disclosures of which are incorporated herein byreference, or, alternatively, a slow pump (e.g., an osmotic pump) can beused.

The unitary daily dosage of the antifolate drug delivery conjugate canvary significantly depending on the host condition, the disease statebeing treated, the molecular weight of the conjugate, its route ofadministration and tissue distribution, and the possibility of co-usageof other therapeutic treatments such as radiation therapy. The effectiveamount to be administered to a patient is based on body surface area,patient weight, and physician assessment of patient condition. Inillustrative embodiments, effective doses can range, for example, fromabout 1 ng/kg to about 1 mg/kg, from about 1 μg/kg to about 500 μg/kg,and from about 1 μg/kg to about 100 μg/kg.

In one illustrative aspect, at least one additional compositioncomprising a therapeutic factor can be administered to the host incombination or as an adjuvant to the above-detailed methodology, toenhance the binding ligand drug delivery conjugate-mediated eliminationof the population of pathogenic cells, or more than one additionaltherapeutic factor can be administered. The therapeutic factor can beselected from a chemotherapeutic agent, or another therapeutic factorcapable of complementing the efficacy of the administered binding liganddrug delivery conjugate.

In one illustrative aspect, therapeutically effective combinations ofthese factors can be used. In one embodiment, for example,therapeutically effective amounts of the therapeutic factor, forexample, in amounts ranging from about 0.1 MIU/m²/dose/day to about 15MIU/m²/dose/day in a multiple dose daily regimen, or for example, inamounts ranging from about 0.1 MIU/m²/dose/day to about 7.5MIU/m²/dose/day in a multiple dose daily regimen, can be used along withthe antifolate drug delivery conjugates to eliminate, reduce, orneutralize pathogenic cells in a host animal harboring the pathogeniccells (MIU=million international units; m²=approximate body surface areaof an average human).

In another embodiment, chemotherapeutic agents, which are, for example,cytotoxic themselves or can work to enhance tumor permeability, are alsosuitable for use in the described methods in combination with thebinding ligand drug delivery conjugates. Such chemotherapeutic agentsinclude adrenocorticoids and corticosteroids, alkylating agents,antiandrogens, antiestrogens, androgens, aclamycin and aclamycinderivatives, estrogens, antimetabolites such as cytosine arabinoside,purine analogs, pyrimidine analogs, and methotrexate, busulfan,carboplatin, chlorambucil, cisplatin and other platinum compounds,tamoxiphen, taxol paclitaxel, paclitaxel derivatives, Taxotere®,cyclophosphamide, daunomycin, rhizoxin, T2 toxin, plant alkaloids,prednisone, hydroxyurea, teniposide, mitomycins, discodermolides,microtubule inhibitors, epothilones, tubulysin, cyclopropyl benz[e]indolone, seco-cyclopropyl benz[e] lindolone, O—Ac-seco-cyclopropylbenz[e] indolone, bleomycin and any other antibiotic, nitrogen mustards,nitrosureas, vincristine, vinbiastine, and analogs and derivativethereof such as deacetylvinbiastine monohydrazide, colchicine,colchicine derivatives, allocolchicine, thiocolchicine, trityl cysteine,Halicondrin B, dolastatins such as dolastatin 10, amanitins such asα-amanitin, camptothecin, irinotecan, and other camptothecin derivativesthereof, geldanamycin and geldanamycin derivatives, estramustine,nocodazole, MAP4, colcemid, inflammatory and proinflarmnatory agents,peptide and peptidomitnetic signal transduction inhibitors, and anyother art-recognized drug or toxin. Other drugs that can be used includepenicillins, cephalosporins, vancomycin, erythromycin, clindamycin,rifampin, chloramphenicol, aminoglycoside antibiotics, gentamicin,amphotericin B, acyclovir, trifluridine, ganciclovir, zidovudine,amantadine, ribavirin, maytansines and analogs and derivatives thereof,gemcitabine, and any other art recognized, antimicrobial compound.

The therapeutic factor can be administered to the host animal prior to,after, or at the same time as the binding ligand drug deliveryconjugates and the therapeutic factor can be administered as part of thesame composition containing the binding ligand drug delivery conjugateor as part of a different composition than the binding ligand drugdelivery conjugate. Any such therapeutic composition containing thetherapeutic factor at a therapeutically effective dose can be used.

The antifolate conjugates described herein can be prepared byart-recognized synthetic methods. The synthetic methods are chosendepending upon the selection of the optionally addition heteroatoms orthe heteroatoms that are already present on the spacer linkers,releasable linkers, the drug, and/or or the antifolate. In general, therelevant bond forming reactions are described in Richard C. Larock,“Comprehensive Organic Transformations, a guide to functional grouppreparations,” VCH Publishers, Inc. New York (1989), and in Theodora E.Greene & Peter G. M. Wuts, “Protective Groups ion Organic Synthesis,” 2dedition, John Wiley & Sons, Inc, New York (1991), the disclosures ofwhich are incorporated herein by reference. In another aspect, theantifolate is attached to the drug via a linker. In one embodiment, thelinker includes an oligopeptide.

In another embodiment, the following illustrative antifolate-linkerintermediate is prepared:

It is to be understood that the foregoing process is illustrative andmay be adapted and modified for the preparation of additionalintermediates described herein.

EXAMPLES

The following illustrative examples are described.

Materials. Pteroic acid (Pte) and N¹⁰-trifluoroacetylpteroic acid wereprepared according to Xu et al., PCT International Application SerialNo. PCT/US2006/009153, filed Mar. 14, 2006. Peptide synthesis reagentswere purchased from. NovaBiochem (La Jolla, Calif.) and Bachem (SanCarlos, Calif.). Folate-free RPMI media (FFRPMI) and PBS were obtainedfrom. Gibco, Grand Island, N.Y. Bovine soluble milk folate bindingprotein (sFBP) was purchased from Scripps (item #F0524). ³H-thymidinewas purchased from Moravek Biochemicals, Brea, Calif. All other commonreagents were purchased from Sigma (St. Louis, Mo.) or other majorsuppliers.

Comparative compounds EC20, EC 119,EC17, EC72, EC140 and EC145 wereobtained from Endocyte, Inc. (West Lafayette, Ind.). Their syntheses,purifications and analytical characterizations have been described indetail elsewhere (Leamon et al. Bioconjugate Chemistry 2002;13(6):1200-10; Lu et al, Cancer Immunol Immunother 2002; 51(3),153-62;Leamon et at Bioconjug Chem 2005; 16(4):803-11 Leamon et al. BioconjugChem 2006; 17(5):1226-32; Vlahov et al. Bioorg Med Chem Lett 2006;16(19):5093-6). Comparative example des-glutamyl CB3717 and antifolate.CB3717 may also be prepared according to known procedures (Jones et al,Eur J Cancer 1981; 17(1):11-9; Jones et al. J Med Chem 1986;29(6)1114-8).

Comparative Example. Synthesis of EC216. In a dry 10 mL round bottomflask, Pte-Cys-OH (7.6 mg, 18.3 μmol) and3-(4-desacetylvinblastinyl)hydrazinecarboxylic acid 2-pyridyldithioethylester (15 mg, 15.3 μM) were dissolved in 0.8 mL of DMSO under argonatmosphere. DIPEA (54 μL, 0.31 mM, 20 equiv.) was added to the abovesolution, and the resulting clear solution was stirred under argon for 3h. Progress of the reaction was monitored by analytical HPLC (10 mMammonium acetate, pH=7.0 and acetonitrile). The reaction mixture wasfiltered and injected on a prep-HPLC column (Waters XTerra C18, 7 μm,19×300 mm). Elution with 1 mM sodium phosphate buffer, pH=7.0 (A), andacetonitrile (B) (method: 1% B to 80% B in 30 minutes at 15 mL/min)yielded pure fractions containing the product. Pure fractions werecombined and acetonitrile was removed under reduced pressure at ambienttemperature. The resulting EC216 conjugate was isolated afterfreeze-drying for 48 h (10 mg, 51%). ¹H NMR (300 MHz, DMSO-d₆ with D₂O)δ 8.63 (s, 1H), 7.58 (d, J=8.7 Hz, 2H), 7.36 (d, J=8.4 Hz, 1H), 7.24 (d,J=8.1 Hz, 1H), 7.10-6.80 (m, 2H), 6.65(d, J=9.0 Hz, 2H), 6.41 (s, 1H),6.19 (s, 1H), 5.68 (m, 1H), 5.56 (d, J=10.2 Hz, 1H), 4.46 (s, 2H),4.35-3.90 (m, 4H), 3.69 (s, 3H), 3.45-2.20 (m, 23H), 2.05-1.85 (m, 2H),1.56 (m, 2H), 1.40-0.95 (m, 8H), 0.78 (t, J=7.5 Hz, 3H), 0.71 (t, J=7.2Hz, 3H); LCMS (ESI): (M+H)⁺=1286.34.

Synthesis of α-t-Butyl-γ-2-(Pyridyl)disulfide-ethyl-L-glutamic diesterEC0614.

Fmoc α-(t-butyl)-L-glutamic acid (1.275 g, 3 mmole),2-(2-pyridyldithio)ethanol (684 mg, 3.0 mmole), DMAP (806 mg, 6.6 mmole)HOBt (450 mg, 3.0 mmole) was dissolved in 150 mL CH₂Cl₂. To the solutionwas added DCC (680 mg, 3.3mmole), the solution was stirred at roomtemperature under argon overnight. The reaction mixture was filtered andthe solvent was evaporated. Toluene was added to dissolve the desiredprodu.ct and then more CH₂Cl₂, the organic solution was washed by NaOAc(0.1M)/10% NaCl (pH=6), then dried over MgSO₄, filtered and evaporatedto give a clear oil. The crude product was put on silica column with 50%EtOAc/50% petroleum ether as eluents to give 1.5 g of product. ¹H NMR(CDCl₃) 8.47-8.44 (m, 1 H), 7.46 (d, J=7.4 Hz, 2 H), 7.68-7.58 (m, 4 H),7.39-7.26 (m, 4 H), 7.10-7.05 (m, 1 H), 5.42 (d, J=8.0 Hz, 1 H),4.40-4.26 (m, 4H), 4.22 (t, J=7.2 Hz, 1 H), 3.03 (s, t, J=6.3 Hz, 2 H),2.50-2.30 (m, 2 H), 2.28-2.18 (m, 1 H), 2.02-1.85 (m, 1 H), 1.48 (s,9H). ¹³C NMR (CDCl₃) 172.7, 171.2, 159.8, 156.2, 149.9, 144.1, 143.9,141.5, 137.26, 127.9, 127.3, 125.3, 121.1, 120.2, 120.1, 82.8, 67.3,62.6, 53.9, 47.4, 37.4, 30.3, 28.2, 28.1

Synthesis of EC282 (CB3717).

Synthesis of N¹⁰-Propargyl-5,8-dideazefolicα-t-Butyl-γ-2-(pyridyl)disulfide-ethyl-diester EC0615.

614 mg of Emoc protected glutamic acid EC: 0614 was dissolved in 12.0mL, DMF, 5,8-dideazapteroic acid (350 mg), PyBOP (510 mg) HOBt(150 mg),DMAP(135 mg) were added to the solution. The reaction mixture was thenstirred for 5 mins, 0.3 mL Et₃N was added and the reaction mixture wasstirred overnight. The reaction mixture was added to NaOAc (0.1M)/10%NaCl (pH=6), centrifuged and got the crude product 601 mg, the crudeproduct was purified by HPLC (10 mM NH₄OAc, pH=5.2 and acetonitrile) togive 360 mg product, ¹H NMR (DMSO-d6) 10.92 (br, 1 H, lactam NH), 8.42(dd. J=4.8, 1.0 Hz, 1 H), 8.23 (d, J=8.7 Hz, 1 H), 7.82-7.70 (m, 5 H),7.47 (dd, J=8.3, 2.1 Hz, 1 H), 7.20 (m, 1 H), 7.13 (d, J=8.7 Hz, 1 H),6.83 (d, J=8.8 Hz, 2 H), 6.28 (br, 2 H), 4.64 (s, 2 H), 4.32-4.19 (m, 5H), 3.19 (t, J=2.2 Hz, 1 H), 3.07 (t, J=6.0 Hz, 2 H), 2.37 (t, J=7.5 Hz,2 H), 2.10-1.83 (m, 2 H), 1.37 (s, 9 H)

Synthesis Of Desacetylvinblastine Hydrazide Derivative EC0616.

39.5 rag of DAVLBH pyridyl disulfide derivative was dissolved in 0.5 mLTHF/0.5 mL H₂O, 4.2 mg of mercaptopropionic acid was dissolved in 0.5 mLTHF/0.5 mL H₂O, the solution was adjusted to pH 7 while purged withargon. Mercaptopropionic acid solution was added to vinblastine solutionand stirred for 20 mins. The reaction mixture was purified on HPLC (10mM NH₄OAc. pH 5.2). 24 mg of product was obtained after lyophilization.LCMS (ESI) 977.38; ¹H NMR (DMSO-d6) 9.39 (s, br, 1H), 9.29 (s, br, 1H),9.12 (s, br, 1H), 8.61 (s, br, 1 H), 7.35 (d, J=8.0 Hz, 1 H), 7.24 (d,J=8.0 Hz, 1 H), 6.99 (t, j=7.0 Hz, 1 H), 6.90 (t, J=7.0 Hz, 1 H), 6.40(s, 1H), 6.18 (s, 1H), 5.67 (dd, J=10.6, 4.7 Hz, 1 H), 5.56 (d, J=10.6Hz, 1 H), 4.21 (t, br, 2H), 4.14-3.90 (m, 3 H), 3.78(s, 1H), 3.70 (s, 3H), 3.50 (s, 3H), 3.38 (s, 2 H), 3.26-3.00 (m, 6H), 3.00-2.87 (m, 5H),2.86 (s, 1H),⁻11), 2.76 (s, 31-1), 271-2.57 (m, 2H), 2.52-2.47 (m, 3H),2.40-2.38 (m, 2H), 2.05-1.88 (m, 2H), 1.70-1.50(m, 2H), 1.38-1.20 (m, 5H), 0.88-0.56 (m, 7H)

Synthesis Of EC0285.

117 mg of EC0615 and 87 mg of thiopeptide in 6.0 mL DMSO, purged withargon, added 0.2 mL DIPEA, after 2 hours, HPLC purification (10 mMNH₄OAc, pH 5.2/acetonitrile) gave 126 mg of product. 90 mg of theproduct was dissolved in 5 mL TFA/TIPS (97.5:2.5) and stirred for 1hour. Then the reaction mixture was added to cold Et₂O, and stirred for10 min. The precipitate was centrifuged and washed with Et₂O threetimes. The reaction afforded 82 mg of white solid. LCMS (ESI) 1073.30;¹H NMR (D₂O) 7.57 (s, 1 H), 7.48 (d, J=9.0 Hz, 2 H), 7.22(d, J8.4 Hz, 1H), 6.88 (d, J=8.7 Hz, 1 H), 6.60 (d, J=9.0 Hz, 2 H), 4.52-4.43 (m, 3 H)4.36-4.30 (m, 2 H), 4.22 (q, J=4.5 Hz, 1 H), 3.98 (s, br, 2 H), J=4.5Hz, 1 H), 3.88-3.73 (m, 2 H), 3.28 (dd, J=14, 9 Hz, 1 H), 3.11 (t, dd,J=14, 9 Hz, 1 H), 2.70-2.48 (m, 8 H), 2.45-2.31 (m, 6 H), 2.28-2.20 (m,2 H), 2.17-2.03 (m, 2 H), 1.96-1.82 (m, 2 H). ^(—)C NMR (D₂O) 181.6,178.5, 178.2, 177.9, 177.8, 175.7, 174.2, 173.5, 168.9, 154.1, 150.2,141.7, 133.9, 122.9, 128.9, 124.6, 121.2, 118.7, 115.8, 112.9, 80.1,73.5, 63.1, 54.9, 54.2, 52.4, 51.7, 41.1, 38.8, 38.7, 38.4, 35.9, 34.8,33.2, 30.9, 30.8, 27.1, 23.3.

Synthesis of EC0284.

22.0 mg of EC0616 in 0.1 mL THF, was added 2.6 mg NHS in 0.1 mL THF, 2.7mg DIPEA in 0.1 mL THF, 11.7 mg of PyBOP in 0.1 mL DMF. The reactionmixture was stirred at room temperature for 40 mins with HPLC monitoringthe reaction. Another equivalent of NHS, DIPEA, PyBOP was added to thereaction and stirred for 40 mins. 16.0 mg of EC0285 was dissolved in 0.5mL H₂O, then adjusted to pH 7.5 by NaHCO₃ aqueous solution, then mixedwith the above reaction solutions. After ½ h. HPLC purification with 1mM phosphate buffer (pH 7) gave 11.2 mg of EC0284 after Lyophilization.LCMS (ESI) (M+H)⁺2033.4; ¹H NMR (DMSO-d6+D₂O) 7.57 (s, 1 H), 7.62 (d,J=8.4 Hz, 2 H), 7.46 (d, J=8.7 Hz, 1 H), 7.34(d, J=7.8 Hz, 1 H), 7.23(d, J=7.8 Hz, 1 H), 7.14 (d, J=8.4 Hz, 1 H), 6.98 (t, J =7.5 Hz, 1 H),6.90 (t, J=7.5 Hz, 1 H), 6.82 C(d, J=8.7 Hz, 2 H), 6.40 (s, 1H), 6.18(s, 1H), 5.67 (dd, 1 H), 5.56 (dd, 1 H), 4.62 (s, br, 2 H), 4.51 (t,J=6.3 Hz, 1 H), 4.36-4.26 (m, 4H), 4.18 (m, 2H), 4.14-3.96 (m, 5 H),3.76 (s, 1H), 3.69 (s, 2 H), :3.26-2.65 (m, 32H), 2.36-1.83 (m, 18H),1.71(m, 6H), 1.64-1.38 (m, 5 H), 1.32-1.13 (m, 13 H), 0.88 -0.56 (m,11H).

Synthesis of αt-Butyl-γ-2-(Pyridyl)disuifide-ethyl Methotrexate EC0619.

To a well stirred solution of pyridyldithio-derivative of glutamic acidEC0614 (50 mg,1eq.) in dry DMF was added4-[N-(2,4-diamino-6-pteridinylmethyl)-N-methylamino]benzoic acid (30 mg,1 eq.). PyBop (48 mg, 1.1 eq.), 1-hydroxybenzotriazole (12 mg, 1.1eq,)and 4-(dimethyiamino)pyridine (11 mg, 1.1 eq.) were added. Afterstirring for 5 min, triethylamine (35 μL, 3 eq.) was added. The reactionmixture was allowed to stir at room temperature for 18 h (TLC, 20% MeOHin CH₂Cl₂). The solvent was removed under reduced pressure. Theα-t-butyl-γ-2-(pyridyl)disulfide-ethyl methotrexate (38 mg) was purifiedby preparative HPLC (10 mM ammonium acetate, pH=7 and acetonitrile).ESI-MS: (M+H)⁺=680.31; ¹H NMR (300 MHz, DMSO-d₆): δ 8.55 (s, 1H), 8.41(dd. 1H), 8.19 (d, 1H), 7.77 (m, 1H), 7.70 (d, 2H), 7.19 (m, 1H), 6.80(d, 2H), 4.76 (s, 2H), 4.28 (m, 1H), 4.20 (t, 2H), 3.19 (s, 3H), 3.06(t, 2H), 2.36 (t, 2H), 1.97 (m, 2H), 1.37 (s, 9H).

Synthesis of γ-2-(Pyridyl)disulfide-ethyl Methotrexate EC0620.

α-t-Butyl-γ-2-(pyridyl)disulfide-ethyl methotrexate EC0619 (20 mg) wasdissolved in 0.5 mL TFA/TIPS solution (97.5% TFA, 2.5% TIPS). Thereaction mixture was stirred for 1 h (analytical HPLC, 10 mM NH₄OAc,pH=7 and acetonitrile), then precipitated in diethyl ether. Theresulting precipitate was washed with diethyl ether (3×), isolated bycentrifugation, and dried under vacuum to afford the crude product (18mg). This yellow powder, γ-2-(pyridyl)disulfide-ethyl methotrexate, wasused in the next step without further purification. ESI-MS:(M+H)⁺=624.32; ¹H NMR (300 MHz, DMSO-d₆): δ 12.58 (br, 1H), 8.69 (s,1H), 8.41 (m, 1H), 8.23 (d,1H), 7.76 (m, 1H), 7.70 (d, 2H), 7.19 (m,1H), 6.80 (d, 2H), 4.85 (s, 2H), 4.35 (m, 1H), 4.19 (t, 2H), 3.23 (s,3H), 3.05 (t, 21), 2.35 (t, 2H), 2.08 (m, 1H), 1.91 (m, 1H).

Synthesis of EC0401.

Fmoc-Glu-O′Bu (30 mg, 1 eq.) was dissolved in dry EtOAc. The solutionwas cooled to −15° C. With stirring under argon,N,N-diisopropylethylamine (26 μL, 2.1 eq,) and isobutyl chloroformate(14μL, 1.5 eq.) were added to this solution. After stirring at −15° C. for45 min, hydrazinecarboxylic acid 2-(pyridin-2-yl-dislfanly) ethyl ester(24 mg, 1.4 eq.) was added. The reaction mixture is stirred at −15° C.for 30min, and then it was allowed to warm to room temperature within 5min. The stirring was continued for an additional 30 min at roomtemperature (TLC, 5% MeOH in CH₂CL₂). The solvent was evaporated todryness. The resulting pyridyldithio-derivative of glutamic acid EC0401(40 mg) was purified on a silica gel column (66% EtOAc in pet. ether),EST-MS: (M+H)⁺=653.1; ¹H NMR (CDCl₃& CD₃OD) δ 8.48 (d, 1H), 7.73 (m,4H), 7.58 (d, 2H), 7.37 (t, 2H), 7.28 (t, 2H), 7.14 (m, 1H), 5.76 (m,1H), 4.35 (t, 2H), 4.32 (t, 2H), 4.18 (t, 1H), 3.01 (t, 2H), 2.24 (m,4H), 1.90 (m, 1H), 1.43 (s, 9H).

Synthesis of Methotrexate-O'Bu-Hydrazide Pyridyldisulfide-ethanolCarhazate EC0402:

To a well stirred solution of pyridyldithio-derivative of glutamic acidEC0401 (45 mg, 1 eq.) in dry DMF was added4[N-((2,4-diamino-6-pteridinylmethyl)N-rnethylamino] benzoic acid (25mg, 1 eq.) followed by PyBop (39 mg, 1.1 eq.), 1-hydroxybenzotriazole(10 mg, 1.1 eq), and 4-(dimethylamino)pyridine (9 mg, 1.1 eq.). After 5min of stirring, triethylamine (29 μL, 3 eq.) was added. The reactionmixture was allowed to stir at room temperature for 18 h. The solventwas removed under reduced pressure. The t-butyl-protectedpyridyldithio-derivative of methotrexate EC0402 (25 mg) was purified bypreparative HPLC (10 mM NH₄OAc, pH=7 and acetonitrile). ESI-MS:(M+H)⁺=738.1; ¹H NMR (DMSO-d6 & D₂O) δ 8.57 (s, 1H), 8.46 (d, 1H), 7.80(m, 2H), 7.73 (d, 2H), 7.24 (t, 1H), 6.81 (d, 2H), 4.79 (s, 2H), 4.22(m, 1H), 4.20 (t, 2H), 3.21 (s, 3H), 3.09 (t, 2H), 2.21 (t, 2H), 2.01(m, 1H), 1.91 (m, 1H), 1.39 (s, 9H).

Synthesis of Methotrexate Hydrazide Pyridyldisulfide-ethanol CarhazateEC0403:

The t-butyl-protected pyridyldithio-derivativeof methotrexate EC0402 (25mg) was dissolved in 0.5 mL of TFA/TIPS solution (97.5% TFA, 2.5% TIPS).The reaction mixture was stirred for 0.5 h then precipitated in diethylether (analytical HPLC, 10 mM NH₄OAc, pH=7 and acetonitrile). Theresulting, precipitate was washed with diethyl ether (3×), isolated bycentrifugation, and dried under vacuum to afford the crude product (18mg). This yellow powder, methotrexate hydrazide pyridyldisulfide-ethanalcarbazate EC0403, was used in the next step without furtherpurification. ESI-MS: (M+H) ⁺=682.3; ¹H NMR (DMSO-d6 & D₂O) δ 8.70 (s,1H), 8.44 (d, 1HI), 7.82 (m, 2H), 7.74 (d, 2H), 7.24 (t, 1H), 6.81 (d,2H), 4.87 (s, 2H), 4.32 (dd, 1H), 4.20 (t, 2H), 3.24 (s, 3H), 3.08 (t,2H), 2.21 (t, 2H), 2.05 (m, 1H), 1.94 (m, 1H).

Synthesis of α-t-Butyl-γ-2-(pyridyl)disulfide-ethyl Aminopterin EC0459.

To a well stirred solution of pyridylchthio-derivative of glutamic acid(95 mg, 1 eq.) in 1 mL dry DMF was added Des-glu-aminopterin (50 mg, 1eq.). PyBop (94 mg, 1.1 eq.), 1-hydroxybenzotriazole (24 mg, 1.1 eq.)and 4-(dimethyl amino)pyridine (22 mg, 1.1 eq.) were added. Afterstirring for 5 min, triethylamine (67 μL, 3 eq.) was added. The reactionmixture was allowed to stir at room temperature overnight (TLC, 20% MeOHin CH₂CL₂). The solvent was removed under reduced pressure, The-t-butyl-2-(pyridyl)disulfide-ethyl methotrexate (45 mg) was purified bypreparative HPLC (10 mM ammonium acetate, pH=7 and acetonitrile).ESI-MS: (M+H)⁺=666.2; ¹H NMR (300 MHz, DMSO-d₆): δ 8.69 (s, 1H), 8.42(m, 1H), 8.19 (d, J=7.7 Hz, 1H), 7.77 (m, 1H), 7.70 (d, J=8.8 Hz, 2H),7.20 (m, 1H), 6.74 (d, J=8.8 Hz, 2H), 4.49 (s, 2H), 4.28 (m, 1H), 4.22(t, J=6.0 Hz, 2H), 3.07 (t, J=6.0 Hz 2H), 2.38 (t, J=7.7 Hz 2H),2.07-1.82 (m, 2H), 1.37 (s, 9H).

Synthesis of γ-2-(Pyridyl)disulfide-ethyl Aminopterin EC0460

α-t-Butyl-γ-2-(pyridyl)disulfide-ethyl aminopterin EC0459 (36 mg) wasdissolved in 0.5 mL, TFA/TIPS solution (97.5% TFA, 2.5% TIPS). Thereaction mixture was stirred for 1 h (analytical HPLC, 10 mM NH₄OAc,pH=7 and acetonitrile), then precipitated in diethyl ether. Theresulting precipitate was washed with diethyl ether (3×), isolated bycentrifugation, and dried under vacuum to afford the crude product (30mg). This yellow powder, γ-2-(pyridyl)disulfide-ethyl aminopterin, wasused in the next step without further purification. ESI-MS:(M+H)⁺=610.1: ¹H NMR (300 MHz, DMSO-d₆+D₂O): δ 8.81 (s, 1H), 8.42 (m,1H), 7.78 (m, 1H), 7.72 (dd, J=8.5 Hz, 2H), 7.20 (m, 1H), 6.74 (d, J=8.5Hz, 2H), 4.60 (s, 2H), 4.36 (q, J=5.0 Hz, 1H), 3.06 (t, J=6.1 Hz, Hz,2H), 2.37(t, J=7.6 Hz, 2H), 2.15-2.01 (m, 1H), 2.00-1.86 (m, 1H).

Synthesis of Aminopterin-O-t-butyl-hydrazide Pyridyldisulfide-ethanolCarbazate EC0468.

To a well stirred solution of pyridyldithio-derivative of glutamic acidEC0401 (104 mg, 1 eq.) in 1 mL dry DMF was added Des-glu-aminopterin (50mg, 1 eq.) followed by PyBop (94 mg. 1.1 eq.), 1-hydroxybenzotriazole(24 mg, 1.1 eq,), and 4-(dimethylamino)pyridine (22 mg, 1.1 eq.). After5 min of stirring, thriethylamine (67 μL, 3 eq.) was added. The reactionmixture was allowed to stir at room temperature for overnight. Thesolvent was removed under reduced pressure. The t-butyl-protectedpyridyldithio-derivative of methotrexate EC0468 (68 mg) was purified bypreparative HPLC (10 mM NH₄OAc, pH=7 and acetonitrile). ESI-MS:(M+H)⁺=724.2; ¹H NMR (DMSO-d6 & D₂O) δ 8.69 (s, 1H), 8.45 (d, J=4.5 Hz,1H), 7.86-7.74 (m, 2H), 7.70 (d, J=8.8 Hz, 2H), 7.24 (t, J=6.2 Hz, 1H),6.73 (d, J=8.8 Hz, 2H), 4.49 (s, 2H), 4.27-4.18 (m, 1H), 3.08 (t, J=6.2Hz, 2H), 3.03-2.97 (m, 2H), 2.22 (t, J=7.6 Hz, 2H), 2.08-1.86 (m, 4H),1.39 (s, 9H).

Synthesis of Aminopterin Hydrazide Pyridyldisulfide-ethanol CarbazateEC0469:

The t-butyl-protected pyridyldithio-derivative of aminopterin EC0468 (33mg) was dissolved in 0.5 mL of TFA/TIPS solution (97.5% TFA, 2.5% TIPS).The reaction mixture was stirred for 0.5 h then precipitated in diethylether (analytical HPLC,10 nM NH₄OAc, pH=7 and acetonitrile). Theresulting precipitate was washed with diethyl ether (3×), isolated bycentrifugation, and dried under vacuum to afford the crude product (30mg). This yellow powder, methotrexate hydrazide pyridyldisulfide-ethanolcarbazate EC0469, was used in the next step without fartherpurification. ESI-MS: (M+H)⁺=668.2; ¹H NMR (DMSO-d6 & D₂O) δ 8.82 (s,1H), 8.44 (d, J=4.7 Hz, 1H), 7.80 (m, 2H), 7.71 (d, J=8.8 Hz, 2H), 7.24(t, J=4.6 Hz, 1H). 6.74 (d, J=8.8 Hz, 2H), 4.60 (s, 2H), 4.32 (dd, J=5.0Hz, 1H), 4.20 (t, J=6.0 Hz, 2H), 3.07 (t, J=6.0 Hz, 2H), 2.22 (t, J=7.8Hz, 2H), 2.15-1.94 (m, 2H).

It is to be understood that foregoing processes may be adapted with theappropriate selection of starting materials to prepare additionalconjugates described herein, such as the following:

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

wherein A is N⁹—CH₃-5-d(i)PteGlu, 5-d(i)PteGlu, IAHQ, BW1843U89,2-NH₂-ZD1694, ZD1694, CB3717, 5-dH₄PteAPBA, 5-dPteHCysA, or DDATHF.

It is understood that in the case of conjugates prepared from antifolatemoieties that do not terminate in an acid function (e.g. 5-dH₄PteOrn),conjugates may be prepared by adding an intervening linker group. Theintervening linker group is selected to contain functional groups thatare capable of forming covalent bonds to the antifolate moiety and thebivalent linker moiety.

METHOD EXAMPLES

Cell culture. Cells were grown continuously as a monolayer usingfolate-free RPMI medium (FFRPMI) containing 10% heat-inactivated fetalcalf serum (HIFCS) at 37° C. in a 5% CO₂/95% air-humidified atmospherewith no antibiotics. The HIFCS contained its normal complement ofendogenous folates which enabled the cells to sustain growth in thismore physiologically-relevant medium (Leamon et al. Proc Natl Acad Sci,USA 1991; 88:5572-6). All cell experiments were performed using FFRPMIcontaining 10% HIFCS (FFRPMI/HIFCS) as the growth medium unlessotherwise specified.

Plate-Based Relative Affinity Assay. One hundred microliters of a FBPsolution (10 μg/mL in PBS) were added to each well of a Reacti-Bind®microtiter plate. Plates were incubated at 4° C. overnight and thenwashed 3 times with cold PBS containing 0.05% Tween-20 (PBS-T). Plateswere equilibrated to room temperature, blocked for 1 h on ice with 100μL/well of freshly-prepared PBS-T containing 0.2% gelatin, and thenwashed 3 additional times with PBS-T. PBS solutions (100 μL per well)containing 100 nM of ³H-FA in the absence and presence of increasingconcentrations of unlabeled FA or EC 145 were added to designated wellsin triplicate. Plates were incubated at 37° C. for 1 with gentle shakingand then rinsed three times with PBS-T. Wells were stripped with 100 μLof acid-saline solution (20 mM sodium acetate, pH 3.0) for up to 20 inat room temperature, and the acidic samples were transferred intoindividual scintillation vials containing 3 mL of cocktail. Wellsexposed to only the 100 nM ³H-FA solution (no competitor) weredesignated as Negative Controls, whereas wells exposed to 100 nM ³H-FAplus 1 mM unlabeled FA served as Positive Controls; DPMs measured in thelatter samples (representing non-specific binding of label) weresubtracted from the DPM values from all samples. Relative affinitieswere defined as the inverse molar ratio of compound required to displace50% of ³H-FA bound to FR on KB cells, and the relative affinity of FAfor the FR was set to 1.

Cell-Based Relative Affinity Assay. The relative affinity of each testarticle was determined based on a method initially described byWesterhoff et al. Mol Pharm 1995; 48:459-71) with modifications.Briefly, FR-positive KB cells were seeded in 24-well Falcon plates andallowed to form adherent monolayers (>75% confluent) overnight inFFRPMI/HIFCS. Spent incubation media was replaced with FFRPMIsupplemented with 10% HIFCS and containing 100 nM of ³H-FA in theabsence and presence of increasing concentrations of unlabeled FA orEC145. Cells were incubated for 1 h on ice or in an incubator at 37° C.(as specified in the figure legends) and then rinsed 3 times with 0.5 mLof PBS. Five hundred microliters of 1% sodium dodecyisulfate in PBS wereadded to each well; after 5 min, cell lysates were collected,transferred to individual vials containing 5 mL of scintillationcocktail, and then counted for radioactivity. Cells exposed to only the³H-FA in FFRPMI (no competitor) were designated as Negative Controls,whereas cells exposed to the ³H-FA plus 1 mM unlabeled folic acid servedas Positive Controls; DPMs measured in the latter samples (representingnon-specific binding of label) were subtracted from the DPM values fromall samples. Relative affinities were defined as described above.

Relative Affinity Assay Format. The in vitro RA assay described withinmeasures a ligand's ability to compete with FA for binding to FRs. Todate, cultured cells have most commonly been used as the FR source.However, herein described is the evaluation of the use of a cell-free,immobilized FR plate system for this assay. This latter method utilizeda microtiter plate to which commercially-available bovine milk solubleFBP had been chemically anchored. Similar to the cell-based method,³H-FA can compete directly with increasing concentrations of testarticle for binding to the attached FRs; however, unlike the cell-basedmethod, bound radiolabel can be conveniently “stripped” from the plateby rinsing with a mildly acidic saline solution. For either assay, arelative affinity (RA) value of 1.0 implies that the test article ligandhas an affinity equal to that of FA for the FR. Likewise, values lowerthan unity reflect weaker affinity, and values higher than unity reflectstronger affinity.

The functionalities of both the cell-and plate-based methods weredirectly compared using EC145, a folate conjugate of the microtubuledestabilizing agent, desacetylvinblastine monohydrazide (DAVLBH; seeTable 1). When evaluated under cold incubation conditions, EC145 wasexperimentally determined to have an RA of 0.19 relative to that of FAfor human FRs (KB cells) and an RA of 0.12 for the plate-anchored bovinemilk sFBP (see FIG. 1). Indeed, the results between the two assays aresimilar (less than a factor of 2). However, considering that (i) the KBcell assay involves the testing with the membrane-bound, human form ofthe FR, (ii) the plate-based assay uses bovine soluble folate bindingprotein, (iii) the plate assay is more expensive to conduct, and (iv)the cell-based assay requires less steps to complete, use of thecell-based assay was adopted for subsequent experiments.

Temperature-Dependent Effects. The effect of incubation temperature onthe relative affinities of a few related pteroates was measured. Asshown in FIG. 2A, pteroic acid (Pte) was experimentally found to have anRA of 0.42, or an affinity 2.4-fold weaker than FA when tested usingcells that were incubated on ice. This value was surprisingly highbecause other published reports had indicated that Pte displayedextremely low affinity for the FR (McHugh et al. J Biol Chem 1.979;254(22):11312-8; Kamen et al. Proc Natl Acad Sci, USA 1986; 83:5983-7).The source of discrepancy between these data and the historical data wasinvestigated. Interestingly, upon repeating this assay at 37° C., the RAof Pte decreased dramatically to 0.01, or an affinity 100-fold weakerthan FA. A similar pattern was also noted for leucovorin (LV; alsocalled 5-formyltetrahydrofolate or folinic acid; see FIG. 2C and D).Additional tests confirmed these findings (data not shown).Interestingly, such temperature-dependent effects were not alwaysobserved when a number of FA-drug conjugates were tested under similarconditions. In fact as shown in FIG. 3, the RAs of both EC72 (amitomycin C conjugate of FA; and EC17 (a fluorescein conjugate of FA;increased with temperature. Subsequent tests were conducted at 37° C.

Serum-Dependent Effects. All of the aforementioned studies wereconducted in the absence of serum. However, it is routine practice toevaluate the activity of folates, FA-drug conjugates, and evenantifolates with cells in the presence of serum. To assess the impactthat serum may have on the RA assay, the cell-associated binding levelof ³H-FA was measured under conditions where the percent serum in themedium was varied. As shown in FIG. 4A, ³H-FA binding to KB cells wasnot found to be affected by fetal bovine serum, even when present at100%. Likewise, increasing the percent sera from 0 to 100% had only aminor effect on unlabeled FA's ability to compete with ³H-FA for bindingto KB cells (see FIG. 4B), the calculated RA values for FA varied byonly 13% among all tested conditions. Interestingly, the RA value forthe desacetylvinblastine monohydrazide FA conjugate, EC145, was found toremain nearly constant at 0.48 (±0.02) when sera was present atconcentrations ≥10%; but, a 2.4-fold decrease in RA was reproduciblyobserved for EC145 when evaluated in the absence of serum (see FIG. 4C).To confirm this latter finding, the RA of a related Vinca alkaloidconjugate, EC140 (see structure in Table 1), was tested under similarconditions. As shown in FIG. 4D, the addition of 10% serum increased theRA of EC140 4-fold, from 0.12 (no serum) to 0.50. Notably, both EC145and EC140 remain stable in 95% serum for incubation periods longer than2 h (via HPLC-UV; data not shown); therefore, degradation and release offree FA from these conjugates is not responsible for these observations.Although the mechanism by which serum improves a FA-drug's RA iscurrently unknown, without being bound by theory, it is possible thatdynamic interactions of the bulky drugs with serum proteins aids in thepresentation of the FA moiety to the binding pocket of the FR. Testmedia including 10% fetal bovine serum were used in the standardconditions for all subsequent RA analyses.

Relative Affinity of Folate Analogs. Employing the defined assayconditions, which included the use of adherent KB cells as the FR sourceand a 10% serum-supplemented medium, a series of folate analogs wereevaluated for their ability to compete for binding with ³H-FA. As shownin Table 1, removal of the Glu residue in FA to produce Pte had caused a91-fold reduction in RA (refer to FIG. 2B). Such results are consistentwith other literature reports. Further removal of the p-aminobenzoylmoiety from Pte was found to completely eliminate competitive bindingcapability, since pterin-6-carboxyllic acid failed to block ³H-FA'sbinding to KB cells at all concentrations evaluated. The most prevalentand natural serum-derived folate, 5-methyltetrahydrofolate (Antony etal. JBC 1985; 260(28):1491 1-7), and its 5-formyl counterpart,leucovorin, were found to display 14-and 125-fold weaker affinities forthe FR, respectively; likewise, the popular anti-folate methotrexate(MTX) showed a 50-fold weaker affinity. CB3717, was found to have an RAvalue equal to that of FA. In contrast, the des-glutamyl analog had anRA value>300-fold lower (see Table 1). These data collectively suggestthat a glutamyl moiety, or at least a hydrophilic moiety, positioned inclose proximity to the p-aminobenzoyl (or aryl) group of the pteroatecontribute to high binding affinity to the FR. Finally, it has beenreported that riboflavin binding protein and FR share ˜27% homology. Asmeasured by the assay described herein, riboflavin's RA to theKB-derived FR is very low. As shown in Table 1, even a 300-fold molarexcess of this vitamin was not able to compete with the binding of ³H-FAto KB cells.

Influence of Drug on Relative Binding Affinity. The production of FAconjugates of drugs that are useful for applications in radiodiagnosticimaging, chemotherapy, immunotherapy and inflammation have beenpreviously reported, as have the RA values for a few of thoseconjugates, including three clinical candidates. However, the assayconditions in those reports were not standardized. Described herein, inTable 2, are the RA values for some previously-reported conjugates aswell as for many new ones that were all tested under standard assayconditions (namely, the use of adherent KB cells as the FR source, and a10%-serum-supplemented 37° C. medium). The drugs in these conjugateswidely varied from a metal-chelating peptide, to potentchemotherapeutics. However, for the most part the RA values all fellwithin a factor of ˜2. Without being bound by theory, it is believedthat this indicates that a flexible molecular spacer placed in-betweenthe FA and drug moieties of the conjugates generally allows forefficient binding of the FA moiety to the FR. It has been found that ashorter spacer decreased the RA value for the desacetylvinblastinemonohydrazide conjugate, EC216 (compare to EC145 in Table 2). However,it is appreciated that the spacer is not the only determinant that canaffect a conjugate's RA, because a recently produced a steroid conjugatewas found to have a 20-fold weaker binding affinity (EC0384; Table 2).

Effect On Transplanted KB Tumors. Mice are injected, subcutaneously withhuman KB tumor cells xenografts. Following a brief three times per week,2-week schedule, animals appeared tumor-free (FIG. 5). The tumors didnot regrow during the entire 110 day study The activity was notaccompanied by any weight loss (FIG. 6), and it was competable with anexcess of co-injected folates (an indicator of FR targeted specificity).

It is appreciated that conducting the binding affinity assays at lowertemperature tends to increase the competitiveness of weaker affinityligands. Accordingly, it is understood that the use of highertemperatures may be better to assess the relative binding affinity, asthe resulting conditions may be more discriminating.

It is appreciated that the presence of serum in the test medium alsoproved to be important to the RA of FA-drug conjugates, but not to FAitself. For example, the RA values for both Vinca conjugates, EC145 andEC140, were shown to dramatically increase in the presence of serum(2.4-and 4.1-fold, respectively). These results could not be explainedby degradation or release of FA from the conjugates because both agentswere subsequently found to remain stable, even in 95% serum, for morethan 2 h. Nonetheless, using a standardized protocol which included theuse of adherent FR-positive KB cells exposed to 100 nM ³H-FA in thepresence of increasing concentrations of competitor in 10%serum-supplemented medium at 37° C., a wide variety of folate analogsand FA-drug conjugates were screened and their RA values determined forcomparison (see Tables 1 and 2).

It is further appreciated that among the folate analogs, it wasinteresting to observe the importance of having a charged moiety inclose proximity to the Pte group. For example, the RA value increased 90to>300-fold when a Glu residue was attached to Pte, and N¹⁰-propargyl5,8-dideazapteroic acid, respectively. Notably, although a Glu residueis most often attached at this position, it is known that other aminoacids can substitute for Glu without dramatically compromising bindingaffinity (Leaman et al. J Drug Targeting 1999; 7(3):157-69; McAlinden etal. Biochemistry 1991; 30:5674-81 Westerhof et al. Proceedings of theAmerican Association for Cancer Research 1991; 32:328). For the seriesof FA-drug conjugates examined, it was found that RA values remainedwithin a factor of ˜2 despite the wide structural variances presentamong the different drugs. But, two exceptions were found. The firstshowed that shortening the peptide-based spacer of EC145 fromγGlu-Asp-Arg-Asp-Asp-Cys down to only a γGlu-Cys residue (in EC216)caused a 10-fold decrease in RA. It is appreciated that eliminating manyof the charged groups in the spacer region may compromise the watersolubility characteristics of the conjugate, but EC216 was observed toremain in solution (even at 30 μM) throughout the assay period.Therefore, without being hound by theory, it is believed that the lowerRA value observed for EC216 may result from steric interference causedby the closer proximity of the drug (DAVLBH) to the Pte unit.

Another exception found was the 20-fold lower RA value which resultedwhen a lipophilic steroid had been linked to folate (EC0384; see Table2). It was found that EC0384 binds serum protein with a value of >96%.The majority of folate conjugates bind serum protein with a value thatis less than 80% (unpublished ob933servations). Without being bound bytheory, it is believed that this factor may, in part, explain the lowerobserved RA.

TABLE 1 Relative Affinity of Ligands at the Folate Receptor (cellassay). Relative Relative Fold Binding Binding Weaker Affinity AffinityAffinity Structure (0° C.) (37° C.) from FA Folic Acid (Pte-Glu)

— 1.000 1.0 Pteroic Acid (Pte)

0.42 0.011 91 Pterin-6- carboxylate

— 0.000 n/a 5-formyl- tetrahydrofolate (folinic acid, Leucovorin)

0.15 (0.1)^((a)) 0.008 125 5-methyl- tetrahydrofolate (5MTHF)

(0.35)^((a)) 0.070 14 Methotrexate (MTX)

 0.000 (0.008)^((a)) 0.018 50 CB3717

— 1.000 1.0 Des-glutamyl CB3717

— 0.002 500 Pemetrexed

0.26 (1.5)^((a)) 0.002 500 ^((a))Westerhoff et al., Mol Pharm48:459-71(1995).

TABLE 2 Relative Affinity of Conjugates for the Folate Receptor (cellassay). Rela- Rela- Fold tive tive Weaker Binding Binding AffinityAffinity Affinity form Comparative Examples (0° C.) (37° C.) FA EC20 —0.92 1.1 (Pte-γGlūβDpr-Asp-Cys)

EC17 0.29 0.45 1.2 (Pte-γGlu-eda-FITC)

EC72 0.53 0.59 1.5 (Pte-γGlu-Cys-L-MMC)

EC140 — 0.50 2.0 (EC119-Hyd-DAVLBH)

EC145 — 0.47 2.1 (EC119-L-DAVLBH)

EC216 — 0.046 22   (Pte-Cys-L-DAVLBH)

Antifolate Conjugate EC0284 — 0.15

What is claimed is:
 1. A method for treating a population of cancercells in a patient, the method comprising administering to the patient atherapeutically effective amount of a conjugate of formula ALDm, whereinA is an antifolate of the formula:

wherein: (1) X═OH, R═H, and Y=Glu; or (2) X═OCH₃, R═H, and Y═Glu; or (3)X═OH, R═H, and Y=Valine; or (4) X═OH, R═H, and Y=Suberate; or (5) X═OH,R═CH₃, and Y=Glu; m is 1 to 3; D is an independently selected drug; and;L is a linker comprising at least one releasable linker; wherein thecancer cells overexpress a folate receptor, and wherein the cancer ischosen from carcinoma, sarcoma, lymphoma, Hodgkin's disease, melanoma,mesothelioma, Burkitt's lymphoma, nasopharyngeal carcinoma, leukemia, ormyeloma.
 2. The method of claim 1, wherein the conjugate is apharmaceutical composition further comprising one or more carriers,excipients, or diluents, or combinations thereof.
 3. The method of claim1, wherein the conjugate binds to a folate receptor on the cancer celland upon binding is internalized into the cancer cell.
 4. The method ofclaim 1, wherein the cancer cells are benign tumor cells, malignanttumor cells, or non-tumorigenic cells.
 5. The method of claim 1, furthercomprising administering another therapy to the patient.
 6. The methodof claim 5, wherein the therapy is surgical removal of a tumor,radiation therapy, chemotherapy, or a biological therapy.
 7. The methodof claim 1, wherein the conjugate is administered in combination with achemotherapeutic agent.
 8. The method of claim 1, wherein the patient isa mammal.
 9. The method of claim 7, wherein the mammal is a human.